JP2005329265A - Tissue heating and ablation system and method using predicted temperature for monitoring and control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for obtaining medical treatment result in a consistent system not causing any contingency by controlling the application of energy for performing body tissue ablation with high reliability while monitoring. <P>SOLUTION: A device for heating body tissue includes: an energy emitting electrode to heat the tissue; a sensing element for measuring the temperature in the electrode part; and a processing element for sampling one or more temperatures measured by the sensing element to derive the temperature estimation for the future time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates generally to systems and methods for creating damage to internal regions of the human body, but under a more limited concept, it is performed for the treatment of heart disease. The present invention relates to a system and method for organ tissue ablation.

BACKGROUND OF THE INVENTION Physicians can now use catheters in medical treatments to reach internal regions of the human body. Further, in some cases, the catheter body has an energy radiating portion at its tip, and ablation of human tissue is also performed.

  In performing these treatments, doctors are required to have stable and uniform control when the energy radiating part comes into contact with the tissue to be ablated. Also, in establishing contact, physicians must carefully add to the elements to transmit energy to the tissue for ablation.

  In performing cardiac tissue ablation using a catheter, the need for subtle control in the emission of energy is an absolute requirement. These so-called electrophysiological treatments are becoming increasingly popular for the treatment of heart rate anomalies called arrhythmias. Typically, cardiac ablation processes create damage to cardiac tissue through the use of radio frequency (RF) energy.

  The main object of the present invention is to apply energy for human tissue ablation with reliable control while monitoring, in a manner that does not cause consistent and unforeseen circumstances, And providing a system and method for obtaining the results.

(Item 1) In an apparatus for heating human tissue, an electrode for radiating energy to heat human tissue, a sensing element for measuring temperature at the electrode part, and measurement by the sensing element A processing element for sampling one or more temperatures and then deriving a temperature prediction for a future time period.
(Item 2) The apparatus for heating human tissue according to item 1, wherein the processing element samples a change in temperature during a period measured by the sensing element to derive a temperature prediction.
(Item 3) The apparatus according to item 1, wherein the processing element generates an output based on the temperature prediction.
(Item 4) The apparatus according to item 3, wherein the processing element generates an output based on a comparison with respect to the specified temperature of the temperature prediction.
(Item 5) The device according to item 4, wherein the specified temperature basically keeps the constant in the period.
(Item 6) The device according to item 4, wherein the specified temperature changes at least once as a function of time.
(Item 7) The apparatus according to item 4, wherein the processing element includes an input for setting a specified temperature.
8. The apparatus of claim 1, wherein the processing element includes an input for setting one or more parameters to derive a temperature prediction.
9. The apparatus of claim 8, wherein the input includes means for changing at least one of the parameters when the processing element derives a temperature prediction.
(Item 10) An apparatus for supplying energy to an electrode for tissue heating, a generator electrically connected to the electrode and adapted to supply energy to the electrode for tissue heating, and A controller connected to the generator for supplying power to the electrodes, and further comprising a sensing element for measuring the temperature at the electrodes, and one or more of which are measured periodically by the sensing element A control device comprising: processing elements that sample temperatures, derive temperature predictions for future periods therefrom, generate signals based on the temperature predictions, and control power supply to the generator; Features device.
(Item 11) The apparatus according to item 10, wherein the processing element compares the temperature prediction with a specified temperature and generates a signal based on the comparison.
(Item 12) The apparatus according to item 11, wherein the specified temperature is continuously the value as it is.
(Item 13) The apparatus according to item 11, wherein the specified temperature is a value that changes at least once as a function of time.
(Item 14) The apparatus according to item 10, wherein the processing element includes an input for setting the specified temperature.
15. The apparatus of claim 10, wherein the processing element includes an input for setting one or more parameters for deriving a temperature prediction.
16. The apparatus of claim 15, wherein the input includes means for changing at least one of the parameters when the processing element samples the temperature and derives a temperature prediction.
(Item 17) The apparatus according to item 10, wherein the processing element averages the temperature prediction.
18. The apparatus of claim 10, wherein the processing element includes a low pass filter element with a constant selection time to average the temperature prediction.
(Item 19) The apparatus according to item 18, wherein the processing line includes an input for setting a time constant of the low-pass filter.
(Item 20) The apparatus according to item 10, wherein the generator supplies the radio frequency energy.
(Item 21) In a device for tissue ablation, a generator electrically connected to an electrode and applied to supply energy to ablate human tissue to the electrode, and a generator connected to the generator to generate electric power And a control element comprising: a sensing element for measuring the temperature at the electrode; a processing element; and the processing element is one or more of which are periodically measured by the sensing element. A first means for sampling the above temperatures and deriving a temperature prediction for a future period therefrom, and a second means for comparing the temperature prediction with a specified temperature and generating a power demand signal based on the comparison. And means for comparing the power demand signal with a signal indicating the power supplied to the generator and A third means for adjusting the power to be fed co-Te, and the processing main ropes composed of a device characterized by comprising the.
(Item 22) The apparatus of item 21, wherein the first means includes an input to set one or more parameters to derive a temperature prediction.
23. The apparatus of claim 22, wherein the input includes means for changing at least one of the parameters when the first means derives a temperature prediction.
(Item 24) The apparatus according to item 22, wherein the second means generates the power request signal based at least in part on the difference between the temperature prediction and the specified temperature.
(Item 25) The device according to item 24, wherein the second means generates the power request signal based on a continuous change of the difference at least to some extent.
(Item 26) The device according to item 25, wherein the second means generates the power request signal based on a rate at which the continuous difference is changed at least to some extent.
(Item 27) The device according to item 21, wherein the specified temperature consists of a value that remains essentially unchanged.
(Item 28) The apparatus according to item 21, wherein the specified temperature is a value that changes at least once as a function of time.
(Item 29) The apparatus according to item 21, wherein the processing element includes an input for setting the specified temperature.
(Item 30) In a method for ablating human body tissue, supplying ablation energy to an electrode; sensing a temperature at the electrode; sampling one or more sensed temperatures; A step of deriving a temperature prediction for the period, and generating a signal for controlling the supply of ablation energy based at least in part on the temperature prediction.
(Item 31) The method according to item 30, wherein the step for generating the signal comprises a comparison of the temperature prediction to a specified temperature and generation of a signal based on the comparison.

SUMMARY OF THE INVENTION The present invention provides a system and method for performing reliable thermal ablation processing of human tissue using temperature sensing.
One aspect of the present invention provides an apparatus and associated method for heating human tissue. This apparatus and method heats human tissue by radiating energy from an electrode. This apparatus and method also measures temperature at the electrode section. This apparatus and method measures one or more temperatures and makes temperature predictions in the future based on them.

  Another aspect of the present invention is that the apparatus and method generates a signal and controls the supply of energy applied to the electrode based at least in part on the temperature prediction.

  In a preferred embodiment, the apparatus and method generates a signal based at least in part on a comparison made between the predicted temperature and the specified temperature.

  The apparatus and method maintain a defined temperature at the electrode section by adjusting the supply of energy applied to the electrode.

  In one embodiment, the specified temperature is a value that maintains a constant while the electrode heats the tissue by emitting energy. In another embodiment, the specified temperature changes at least once while the electrode emits energy and heats the tissue.

  This device and method embodies the features of the present invention and is well suited for use in the field of cardiac ablation. The apparatus and method can also be used in heat ablation of other tissues. For example, the various aspects of the present invention can be applied to performing tissue ablation in the prostate, brain, gallbladder, uterus, and other areas of the body using systems that are not necessarily catheter based.

  Other features and advantages of the invention are described in the following description and drawings, as well as the appended claims.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a system 10 for performing human tissue ablation, embodying features of the present invention.
In the illustrated embodiment, the system 10 has a generator 12 that emits radio frequency energy and performs tissue ablation. Of course, other types of energy can serve the purpose of tissue ablation.

  The system 10 also has a steerable catheter 14 with an ablation electrode 16 that emits radio frequency. In the illustrated embodiment, the ablation electrode 16 is made of platinum.

  In the illustrated embodiment, the system 10 operates in a unipolar mode. In this configuration, the system 10 has a skin patch electrode that serves as the second neutral electrode 18. In use, the neutral electrode 18 is affixed to the patient's back or other skin portion.

  Alternatively, the system 10 operates in bipolar mode. In this mode, the catheter 14 includes both electrodes.

  Although the system 10 can be utilized in a variety of environments, it is described herein as the system 10 when used on cardiac ablation therapy.

  In use for this purpose, the physician manipulates the catheter 14 and through the main vein or artery (typically the femoral vein or femoral artery) to the internal region of the heart that requires treatment. Further, the doctor operates the catheter 14 to place the electrode 16 in a portion that contacts the tissue in the heart to be ablated. A user applies radio frequency energy from the generator 12 through the electrode 16 to ablate and form damage on the contacted tissue.

I. Ablation Catheter In the embodiment shown in FIG. 1, the catheter 14 has a distal tip 24 with a handle 20, a guide tube 22, and an electrode 16.

  The handle 20 includes a steering mechanism 26 for the catheter tip 24. The cable 28 extends from the rear of the handle 20 and has a plug (not shown). This plug connects to the catheter 14 and extends to the generator 12 to conduct radio frequency energy to the ablation electrode 16.

Left and right steering wires (not shown) extend through the guide tube 22 and interconnect the steering mechanism 26 with the left and right sides of the tip 24. When the steering mechanism 26 is rotated to the left, the left steering wire is pulled and the tip 24 bends to the left. When the steering mechanism 26 is rotated to the right, the right steering wire is pulled and the tip 24 bends to the right.
In this way, the doctor manipulates the ablation electrode 16 to contact the tissue to be ablated.

  Details of the steering mechanism for this and other types of ablation elements 10 are disclosed in US Pat. No. 5,254,088 to Lunquist and Thompson, which is included herein for reference. ing.

A. Temperature Sensing As shown in FIGS. 2-4, the ablation electrode 16 includes at least one temperature sensing element 30. As will be described in more detail below, the power that generator 12 applies to electrode 16 is set at least in part by the temperature conditions sensed by element 30.

  In the embodiment shown in FIGS. 3 to 4, the ablation electrode 16 has a cylinder 32 inside the tip of the tip. The temperature sensing element 30 occupies a space in the cylinder 32.

  In FIGS. 3-4, the temperature sensing element 30 has a bead-shaped thermistor 34 associated with two lead wires 36 and 38. The temperature sensing tip of the thermistor 34 is exposed at the tip end of the ablation electrode 16 during tissue contact. The thermistor 34 type can be purchased from Fenwal Co. of Massachusetts as product number 111-202CAK-BD1. The lead wires 36 and 38 are made of # 36 AWG signal wire Cu + clad steel (strong insulator).

  The thermistor 34 and lead wires 36 and 38 including the electrode cylinder 32 are covered with a potting composition 40. Lead wires 36 and 38 are further shielded by an insulating sheath 42. Both the composite 40 and the sheath 42 electrically insulate the thermistor 34 from the ablation electrode 16 surrounding it.

  The potting compound 40 and the insulating sheath 42 can be manufactured from various types of materials. In the illustrated embodiment, the Loctite adhesive serves as the potting composition 40. However, other sianoacrylate adhesives, RTV adhesives, polyurethanes, epoxies, and other similar ones may be used. The sheath 42 is made of polyamide, but other materials can be used as long as they are general electric insulation materials.

  In the preferred embodiment shown, the thermal insulation tube 44 further encloses the thermistor 34 and lead wires 36 and 38. The heat insulation tube 44 can be joined to the inner wall of the cylinder 32 like an adhesive by itself.

  There are various thermal insulation materials for the tube 44. In the illustrated embodiment, the material is polyamide and occupies about 0.003 inches of wall thickness. Other heat insulating materials such as Mylar or Capeton can also be used.

The lead wires 36 and 38 of the thermistor 34 pass through the guide tube 22 and into the catheter handle 20. At that point, the lead wires 36 and 38 are electrically connected to the cable 28 extending from the handle 20. The cable 28 is connected to the generator 12 and transmits a temperature signal from the thermistor 34 to the generator 12.
In the preferred embodiment shown (as FIG. 10 shows), the handle 20 comprises a thermistor 34 calibration element R _CAL . The element R _CAL is considered a deviation in nominal resistance among various thermistors. During the manufacturing process of the catheter 10, the resistance of the thermistor 34 is adjusted to a known temperature, for example, 75 degrees Celsius. The calibration element R _CAL has a resistance value equal to the adjustment value. Details will be described later.

II. RF Generator As shown in FIG. 5, the generator 12 has a radio frequency power source 48 connected to a power line 52 and a return line 54 through a main isolation transformer 50. The power line 52 reaches the ablation electrode 16, and the return line 54 extends from the neutral electrode 18.

  In the illustrated embodiment, the power source 48 is typically tuned to deliver up to 50 watts at a 500 kHz radio frequency when utilized for cardiac ablation.

The generator 12 further comprises a first process stage 56. The first process stage 56 receives as input values an instantaneous power signal P _(t) , a set temperature value T _SET and a temperature control signal T _CONTROL . Analyzing these input values based on specified criteria, the first process stage 56 derives the required power signal P _DEMAND .

The generator 12 also has a second process stage 58. The second process stage 58 receives the required power signal P _DEMAND from the first process stage 56 as an input value. The second process stage 58 also receives the instantaneous power signal P _(t) and the maximum output value P _MAX as input values. Analyzing these input values based on specified criteria, the second process stage 58 adjusts the amount of power generated, expressed as P _(t) , by adjusting the magnitude of the radio frequency voltage of the power source.

  It is desirable that the generator 12 has the interactive user interface 13 shown in FIG. The interface 13 is sufficiently usable as a normal means such as a normal input device (for example, a keyboard or a mouse), an output display device (for example, a graphic display monitor or CRT), and an audio and visual alarm. ing.

A. First process stage
The input value of the power signal P _(t) generated for the first process stage 56 is generated by the multiplier 60. The multiplier 60 receives the instantaneous current signal I _(t) from the separated current sensing transformer 62 and the instantaneous voltage signal V _(t) from the separated voltage sensing transformer 64.

The isolation current sensing transformer 62 is electrically connected to the return line 54. The transformer 62 measures the instantaneous radio frequency current I _(t) emitted by the ablation electrode 16, passing through the human tissue and reaching the neutral electrode 18.

The isolation voltage sensing transformer 64 is electrically connected between the power supply line 52 and the return line 54. The voltage sensing transformer 64 measures the instantaneous radio frequency voltage V _(t) between the ablation electrode 16 and the neutral electrode 18 across the body tissue.

The multiplier 60 multiplies I _(t) and V _(t) to obtain an instantaneous radio frequency output P _(t) that passes through the low-pass filter 61 and removes fine waves. The filtered P _(t) serves as an input signal for the output to the first process stage.

In the preferred embodiment shown, the generator 12 has a display 110 (see also FIG. 1 ₎ for displaying P _(t) as part of its overall interface 13.

The set temperature value T _{SET that} is sent to the first process stage can be entered by the physician through an interface 66 that is part of the overall interface 13 of the generator 12 (see also FIG. 1). The set temperature value T _SET represents the temperature that the physician requires to maintain at the ablation site. The value T _SET can be established in other ways. For example, the value T _SET shows various values over time as shown in the set temperature curve. More details on this will be given later.

The set temperature value T _SET is selected based on the required therapeutic loss characteristics. Typical therapeutic damage characteristics are the surface area of the tissue to be ablated and the depth of ablation. A typical set temperature T _SET ranges from 50 ° C to 90 ° C.

The input of the temperature control signal T _CONTROL is based on T _{M (t)} sensed by the sensing line 30 as an actual instantaneous temperature state.

In the embodiment shown in detail, the first process stage 56 receives the resistance value output from the thermistor 84 as the T _CONTROL (ohm value). This resistance value is divided by the calibration value R _CAL to standardize the resistance value of the thermistor 34.
This standardized resistance value includes the stored temperature data of the thermistor and serves as an input value to a read only memory (ROM) table in the generator 12. The output of this ROM is the actually measured temperature _{TM (t)} (Celsius).

The output of TM _(t) is preferably displayed on a display 68 that is part of the overall interface 13 of the generator 12 (see also FIG. 1).

The actual instantaneous temperature T _{M (t)} can be used directly by the first process step 56. However, in the illustrated preferred embodiment, the first process stage 56 includes a predictive temperature processor 70 (PTP). The PTP 70 obtains a predicted temperature value (designated as T _{PRED (t) )} from T _{M (t)} .

(I) Predictive temperature processor
PTP 70 continuously samples T _{M (t)} from a specified sample period ΔT _SAMPLE . By applying the specified criteria to this sample, PTP 70 should be at the end of the future period (greater than ΔT _SAMPLE ) at the end of each sample period, assuming that the power supplied to the ablation electrode 16 is unchanged. The temperature state T _{PRED (t)} is predicted. This future period is called the forecast period ΔT _PREDICT .

The length of the prediction period ΔT _PREDICT can take various values. The maximum length is largely due to the thermal time constant of the tissue, which takes into account the physiological response that the tissue is supposed to cause with respect to the temperature state generated during ablation. The predicted period ΔT _PREDICT should not be longer than the period during which the cells of the tissue are expected to be altered by exposure to ablation heat.
The thermal time constant in the case of heart tissue does not exceed about 2 seconds as the longest typical of the prediction period ΔT _PREDICT . After about 2 seconds, it is conceivable that the cell tissue begins to deteriorate in the heart tissue by being exposed to a region of temperature generated during ablation.

ΔT _SAMPLE is selected to be smaller than ΔT _PREDICT . PTP 70 measures the instantaneous temperature T _{M (t)} at the end of the current sample period, where n is the number of previous sample periods selected for comparison, it is one or more previous samples. Compare with the temperature measured at the end of period T _{M (tn)} . Based on the change in temperature measured during the selected sample period and taking into account the relationship between the amount of ΔT _SAMPLE and ΔT _PREDICT , PTP 70 predicts T _{PRED (t)} according to:

here,

Further, i = 1 to n.

In an exemplary embodiment of PTP 70 in cardiac ablation, ΔT _PREDICT is selected as 0.48 seconds. ΔT _SAMPLE is selected as 0.02 seconds (50 Hz sampling rate). Therefore, in this embodiment, K = 24.
Further, in this example, n is selected as 1. In other words, the PTP 70 treats T _{M (t)} as an instantaneous sample period (t) and treats T _{M (t−1)} as the preceding sample period (t−1).

In this embodiment, the PTP 70 derives T _{PRED (t)} from the following equation.

T _{PRED (t)} = 25T _{M (t)} -24T _{M (ti)}
In the preferred embodiment shown, the PTP 70 includes a low pass filter 72 having a selected time constant (γ). The PTP 70 averages T _{PRED (t)} through the filter 72 before being fed to the demand output processor DPP 76 described below.

  The time constant (γ) of the selected filter 72 shows various values depending on the required accuracy. In general, the required accuracy can be obtained with a time constant (γ) in the intermediate region of about 0.2 seconds to about 0.7 seconds. In the exemplary embodiment described above, a time constant (γ) of 0.25 seconds is used.

The degree of accuracy of the PTP 70 is also changed by K taking various values. More specifically, when the value of K is lowered, it is possible to expect higher accuracy in the PTP 70 in predicting the future temperature T _{PRED (t)} . The value of K becomes various values by selecting the value of ΔT _SAMPLE or ΔT _predict or both. It is desirable that the value of K is changed by the selected ΔT _predict .

The degree of accuracy PTP 70 can be improved by choosing a better value of n as required. It is only necessary to take a value retroactive to the past of T _{M (t)} in the calculation of T _{PRED (t)} .

In the preferred embodiment shown, the PTP 70 includes a user interface 74 that is part of the overall interface 13 of the generator 12 (see FIG. 1). Using this interface 74, the doctor can select and update the sampling history (n), the prediction period ΔT _PREDICT and the time constant (γ) in real time online.

As discussed in more detail below, the ability of the PTP 70 to vary the accuracy in calculating the on-line changing T _{PRED (t)} allows flexibility for various ablation conditions in the first process stage 56. Adaptation is made.

(Ii) Request output processor (DPP)
The first process stage 56 further has a demand output processor (DPP) 76. The DPP 76 periodically compares T _{PRED (t)} with the set temperature value T _SET . Based on this comparison result and considering the instantaneous output amount P _(t) supplied to the ablation electrode 16, the DPP 76 derives the required power output P _DEMAND . The DPP 76 also takes into account operational goals and criteria such as other system response times, errors in steady temperature conditions, and maximum temperature exceeded.

The required power output P _DEMAND of the first process stage 56 indicates the amount of radio frequency output that is supplied to the ablation electrode 16 and that is to establish or maintain the required local temperature state T _SET at the ablation electrode 16.

There are various ways in which DPP 76 derives P _DEMAND . Examples include proportional control principles, proportional-integral-derivative (PID) control principles, adaptive control, neural networks, and fuzzy logic control principles.

(A) In the preferred embodiment that has been modified PID control illustrated using fixed T _SET, DPP76 is particularly adopted corrected speed PID control techniques as applied to the cardiac ablation. By using this technique, DPP 76 controls the amount of P _DEMAND based on the constant of T _SET established by the physician.

In the preferred illustrated embodiment, the DPP 76 compares the derived operating value V ₀ with a pre-selected set value (V _s ) for operating conditions. Based on this comparison, DPP 76 establishes an error signal (Δ) by:

Δ = V _S −V _D DPP 76 transmits a power demand signal for the next period P _{DEMAND (t + 1)} based on a nonlinear function of the current and past values of error signal Δ shown below. .

P _{DEMAND (t + 1)} = f (Δ ₁ , Δ ₂ , Δ ₃ ,..., Δ _n )
As common general knowledge, f is a non-linear function of N variables that the DPP 76 follows when executing its processing function. Δ ₁ , Δ ₂ , Δ ₃ ,. . . , Δ _n are the values of the error signal Δ at each of the N moments. DPP 76 therefore adjusts the power by an increase based on a nonlinear function of the current and past values of error signal Δ.

  More specifically, in the illustrated preferred embodiment, at the end of each sample period (t), DPP 76 derives the required power output required for the next sample period (t + 1) by the following equation: .

P _{DEMAND (t + 1)} = P _(t) + S [αE _(t) −βE _(t−1) + δE _(t−2) ]
At this time, the nonlinear function f (Δ) is expressed by the following equation.

f (Δ) = S [αE _(t) −βE _(t−1) + δE _(t−2) ]
The error Shindan Δ is expressed as E _(t) . At this time, V _O = T _PRED and V _S = T _SET , so that E _(t) = T _SET −T _{PRED (t)} . In this embodiment, when T _{PRED (t)} is determined by the PTP 70, the starting value of T _SET that is essentially intact is selected.

Α, β, and δ are proportional constants K _p (related to the magnitude of the difference), integer constants K _i (related to changes in the difference at the end), and derived constants K _d (change rate of the difference at the end). It is assumed to represent a normal speed PID based on ΔT _SAMPLE is given by the following equation.

S is the selected scaling factor, and its value follows the following formula _whether T _{PRED (t)} is larger or smaller than T _SET .

S = X, where E _(t) > 0 (ie T _SET > T _{PRED (t)} )
S = Y, where E _(t) <0 (ie, T _SET <T _{PRED (t)} )
Further, the value of S is asymmetric, that is, it is most desirable that X is different from Y and that Y> X.

From the above relationship, it is assumed that the desired error E _(t) should be maintained as zero.
Other desired error values can be used. By utilizing an asymmetric scaling factor S, the desired nonlinear response f (Δ) continuously maintains the desired error E _(t) .
In maintaining desire of the error E _(t) to zero, DPP76 of f (delta) decreases the faster power than increasing power (when _{T PRED (t) <T SET} ) (T PRED (t _{) When} > T _SET ).

In the preferred embodiment shown, DPP 76 uses fixed values K _p , K _i and K _d as coefficients and ignores special ablation conditions.

By adjusting the initial calculation of T _{PRED (t)} by PTP 70 for changing ablation conditions, the calculation of P _DEMAND can be applied by the physician online. Thanks to the flexibility of on-line adjustment by the PTP 70, a complicated table of K _p , K _i and K _d values need not be placed in the system to accommodate changes in ablation conditions.

The following K _p , K _i, and K _d values have been determined to be possible for use with DPP 76 among the applicators.

K _p = 0.025375 K _i = 97.0695 K _d = 7.82 × 10 ⁻⁵
In an exemplary embodiment of DPP 76, ΔT _SAMPLE = 0.02,
Therefore, α = 0.999998 β = 0.93750 δ = 3.91 × 10 ⁻³ .

In this exemplary embodiment of DPP 76, S = 2.0, where E _(t) > 0 (ie, T _SET > T _{PRED (t)} )
And S = 8.0, where E _(t) <0 (ie, T _SET <T _PRED )
It is.

In this exemplary embodiment, if there is no limit to the power that can be used, P _{DEMAND (t)} is adjusted to reach T _SET ± 3 ° C. within 5 seconds. It is also intended to keep the peak steady state temperature error (defined as T _SET -T _{PRED (t))} below 3 ° C. The example also continuously adjusts P _{DEMAND (t)} to avoid exceeding T _SET above 3 ° C.

(B) Modified PID control using various T _SET
In an alternative embodiment, DPP 76 controls the amount of P _DEMAND based on a continuous change in T _SET by utilizing the previously described modified speed PID control. In this example, T _SET is expressed as a function of time, linear or non-linear (see FIGS. 6A and 6B). In this example, T _SET consists of a curve with respect to time of temperature when tissue is heated (see FIGS. 6A and 6B). The curve has a first temperature value set in the first period and a heating temperature value set in the second period after at least another first period.

As FIG. 6A shows, T _SET can be expressed in the term of the linear function at the beginning of the ablation process (eg, 5 seconds of start). From t = 0 seconds to t = 5 seconds, the value of T _SET increases linearly with a progressively selected slope. At t = 6 seconds, T _SET begins to _appear non-linear, and the T _SET is preselected and the slope flattens as it approaches the final control value for ablation.

In an alternative embodiment (shown in FIG. 6B), T _SET adapts the thermal mapping prior to thermal ablation to show a complex curve. As shown in FIG. 6B, from t = 0 seconds to t = 2 seconds, the value of T _SET increases linearly with a progressively selected slope. t = T _SET at 3 seconds at the beginning is represented as a non-linear function, T _SET slope flattens with approximation to the first pre-selected value of the thermal mapping. The gradient remains flat until t = 10 where again the value of T _SET begins to increase linearly with the progressively selected gradient. At t = 13 seconds, T _SET again begins to be expressed as a non-linear function, and T _SET approximates the second preselected tissue ablation value and the slope becomes flat. In the example shown in FIG. 6B, the first value of T _SET thermal mapping ranges from 45 ° C. to 50 ° C., while the second value of T _SET for tissue ablation ranges from 50 ° C. to 90 ° C. And around 70 ° C. is desirable. Furthermore, T _SET can be shown as a true function of time.

In either the embodiment of FIG. 6A or FIG. 6B, DPP 76 receives as an input a continuously changing value of T _SET indicative of a specified set temperature curve. System derives P _DEMAND by calculating E _(t) based on the value of change in them in the same way as to derive the P _DEMAND based upon a constant value of T _SET.

(C) Adaptive control system
FIG. 7 shows an alternative embodiment of DPP 76 that derives P _DEMAND using adaptive control principles. In this embodiment, DPP 76 receives T _SET and T _PRED as input in the manner described above. The value of T _SET can be fixed as described above or can be changed with time.

  In the embodiment of FIG. 7, DPP 76 further has a pair of adaptive filters 78 and 80. Both filters 78 and 80 produce an output based on the input expressed assuming the relationship between them. In the illustrated embodiment, the output consists of an estimate of the external state that DPP 76 independently measured based on the assumed relationship. The DPP 76 compares the estimated output value with the actually measured external state, and adjusts the coefficient of the assumed relationship, thereby minimizing the error between them.

In the DPP 76 embodiment shown in FIG. 7, filter 78 receives as input an instantaneous power P _(t) applied to ablation electrode 16 by RF source 48. Filter 78 receives as output the assumed relationship between P _(t) and P _(t) and the temperature T _(t) at the ablation site, and approximates the temperature state T _{SET (t)} that the sensing element 30 should sense. Generate a value. As a result, the filter 78 approximates the heat transfer function as the tissue contacts the ablation electrode 16.

DPP76 includes summing junction 82 to derive a temperature error signal T _E by subtracting from the temperature T sensed actually at sensing element 30 to estimate the temperature _{T EST (t) (t)} . The DPP 76 feeds back the error signal T _E to the filter 78. Filter 78 is to minimize the amount of error T _E to adjust the assumed coefficient of relations between P _(t) and T _(i).

In the preferred embodiment, filter 78 utilizes a finite linear sequence to represent the assumed relationship between P _(i) and T _(i) . The numerical sequence approximates the future temperature T _{EST (t + 1)} based on the current instantaneous power P _(t) and the past power P _(tn) . Note that n represents a numerical value regarded as a past power state. The quantity n can take various values depending on the required situation.

In the illustrated embodiment, the filter 78 considers the current power P _(t) and the preceding power P _(t-1) (ie, n = 1). In this example, the finite linear sequence is represented as follows:

T _{EST (t + 1)} = aP _(t) + bP _(t-1)
At this time, a and b represent assumed transfer coefficients.

Assuming the transfer factor is initially composed of selected value is adjusted at that time to minimize the error signal T _E. This adaptive adjustment can be achieved by utilizing various known techniques. For example, the coefficients can be adjusted by based on the least mean square (LMS) method which tends to minimize the square error T _E.

  The LMS method updates the coefficients a and b according to the following formula:

T _{E (t)} = T _(t) −T _{EST (t)} a _{(t + 1)} = a _(t) + μP _(t) T _{E (t)} b _{(t + 1)} = b _(t) + μP _{(t -1)} T _{E (t)}
At this time, μ is the number of steps of the algorithm.

  The larger μ is, the faster the convergence rate is, but the wavelength for the optimum coefficient is also increased. Also, as μ decreases, the convergence rate and the wavelength for the optimum coefficient are reduced. The optimal value of μ depends on the characteristics of the modeled system. For the illustrated electrode-bio-tissue system, μ is between 0.01 and 0.5.

Filter 80 is the inverse of filter 78. The filter 80 receives as an input the temperature error signal ΔT generated by the summing junction 84. Summing junction 84 subtracts T _{PREDICT (t)} from T _SET to generate error signal ΔT.

The filter 80 approximates how much the power P _(t) should be corrected taking into account ΔT based on the reciprocal of the hypothetical relationship between the power P _(t) used by the filter 78 and the temperature T _(t) as output. ΔP indicating the value is generated. The relationship utilized by the filter 80 in relation to the hypothesized relationship provided to the filter 78 is approximated using the second order Taylor series:

Filter 80 minimizes the amount of error signal T _E by adjusting its coefficients in relation to the adjustments that filter 78 made to coefficients a and b based on error signal T _B at summing junction 82. .

Its output ΔP of the filter 80 is initialized to the starting power level P ₀ at the beginning of the ablation process and supplied through another summing junction 86. The summing junction 86 continuously adjusts the starting power value together with the ΔP output of the reciprocal filter 80. The output of summing junction 86 will consequently consist of P _DEMAND .

The DPP 76 shown in FIG. 7 sends the output P _DEMAND to the second process stage 58 to modify P _(t) .

(D) Neural network predictive control
The temperature measured by the sensing element 30 for a particular heat exchange condition between the tissue cell and the metal ablation electrode 16 in contact therewith does not necessarily match the actual maximum tissue temperature. This is because the hottest point is about 0.5 mm to 1.0 mm from where the electrode 16 (and also the sensing element 30) radiating thermal energy directly below the surface of the tissue contacts the tissue. . If power is applied to the tissue too rapidly, the actual maximum tissue temperature in this local area will exceed 100 ° C., causing the tissue to dry.

FIG. 11A shows an alternative embodiment of DPP 76 that derives P _DEMAND using neural network control principles. In this embodiment, the PTP 70 receives the predicted temperature value of the highest temperature tissue local T _{MAXPRED (t)} from the neural network prediction instrument 200 as an input. DPP 76 derives P _{DEMAND (t + 1)} based on the difference between T _{MAXPREDICT (t)} and T _SET . The value of T _SET may be fixed, but may take various values as time passes as described above.

In this embodiment, the prediction instrument 200 consists of a two-layer neural network, although some layers are still hidden. This prediction instrument 200 receives as input a set of past temperature samples K sensed by element 30 ( _{TM (t-k + l)} ). For example, in the case of sampling for a period of 0.02 seconds and following the past 2 seconds, K = 100.

Predictive instrument 200 includes first and second hidden layers, four neurons, and designated N _(LX) . L identifies layer 1 or layer 2, and X identifies neurons on the layer. The first layer (L = 1) has 3 neurons (X = 1 to 3), followed by N _(1.1) , N _(1.2) and N _(1.3) . The second layer (L = 2) consists of one output neuron (X = 1) and is designated N _(2.1) .

The past sample loaded with sensing element 30T _{M (t-i + l)} (i = 1 to K) is obtained from each neuron N _(1,1) , N _(1,2) and N _{(1 , 3)} as input. FIG. 11 represents the loaded input sample as W ^L _{(k, N)} . At this time, L = 1, k is the sample order, and N is the input neuron number 1, 2, or 3 in the first layer.

The second layer output neuron N _(2,1) receives as input the weighted outputs of neurons N _(1,1) , N _(1,2) and N _(1,3) . FIG. 11 represents the loaded output as W ^L _(ox) . Here, L = 2, o is the first layer output neuron 1, 2 or 3, and x is the second layer input neuron number 1. Based on these weighted inputs, output neuron N _(2,1) predicts T _{MAXPRED (t)} .

The prediction instrument 200 must be learned on the basis of a known data set obtained experimentally in advance. For example, using the back-propagation model, the prediction instrument 200 can be learned to predict based on the highest known temperature of the data set with the smallest error. When the learning process is complete, the prediction instrument 200 is available for predicting T _{MAXPRED (t)} .

As shown in FIG. 11B, in the first process step 56, it is possible to derive P _{DEMAND (t)} using a single neural network 201. In this embodiment, network 201 receives as input the value of T _SET and power P _(t) in addition to the past samples of temperature k from sensor 30. The network 201 derives as output P _{DEMAND (t)} that reflects the required power level that maintains the highest predicted temperature at or near T _SET . Before starting, a set of data including solutions based on all of the requested inputs is necessary for the neural network of the predictive instrument 201 to learn to manipulate the inputs and obtain the required output at the minimum amount of error. is there.

(E) Fuzzy Logic Control FIG. 12 shows an alternative embodiment of the first process stage 56 that derives P _DEMAND using fuzzy logic control principles. In this embodiment, the first process stage 56 has a fuzzification device 202 that receives the temperature signal T _{M (t)} from the sensor 30 as an input.
The fuzzifier 202 also receives T _SET as an input constant value or a continuously changing value. The fuzzy digitizer 202 converts the input data of T _{M (t)} into a fuzzy input based on the relationship with T _SET in the relational principle. For example, the fuzzy input can determine the degree (or membership function) in comparison with T _SET for T _{M (t)} such as “cool”, “warm”, “warmer”, and “hot”.

  The fuzzy input is passed through an I / O mapper 204 that translates the input into a fuzzy output by translating it into a power descriptive label. This serves the purpose by utilizing the “if-then” rule of the language, eg expressed as “if fuzzy input = ... then fuzzy output = ...”. Alternatively, more complex mapping matrix operations can be used.

For example, if T _{M (t)} is “cool”, 1 / O mapper 204 outputs a descriptive label “maximum positive” to indicate that a relatively large increase in power is sought. Similarly, if T _{M (t)} is “hot”, I / O mapper 204 outputs a descriptive label “maximum negation” to indicate that a relatively large reduction in power is desired. Intermediate fuzzy inputs “Warm” and “Warmer” produce intermediate descriptive labels such as “Minimum positive” and “Minimum negative” as fuzzy outputs.

These fuzzy outputs are passed through the defuzzifier 206. The defuzzification device 206 receives as inputs actual power P _(t) of from the fuzzy output is related to the amount of change in P _(t). The defuzzification device 206 derives P _{DEMAND (t)} based on the change amount of the request based on P _(t) and the fuzzy output.

  In order to refine the relational set and rules of the I / O mapper 204, it is desirable that the fuzzy logic controller be learned based on the known data set before use.

B. Second process stage
In the preferred embodiment shown, the second process stage 58 (see FIG. 5) has a converter 112. The converter 112 derives a command voltage wet sign V _{DEMAND (t)} based on the power input signal and adjusts the magnitude V _(t) of the voltage supplied to the source 48, resulting in the adjustment of P _(t). Is done. Alternatively, the converter 112 can derive a command current signal I _{DEMAND (t)} based on the power input signal and adjust the magnitude of the current supplied to the source 48 to achieve an equivalent result. It is.

(I) Power reduction stage
In one embodiment, the power input to converter 112 can also consist of P _{DEMAND (t)} as derived to DPP 76. In the preferred embodiment shown, the second process stage 58 includes a power requirement reduction stage 94 between the DPP 76 and the converter 112. The power reduction stage 94 receives P _{DEMAND (t)} as an input and takes the modified demand power signal MP _{DEMAND (t)} into account, taking into account one or more other operating conditions being performed at that time. , Generate. Converter 112 receives MP _{DEMAND (t)} as its input.

More specifically, the power reduction stage 94 monitors whether the electrode is in a reliable operating state. The power reduction stage 94 compares the monitored state with a predetermined criterion as the second operating state, and sends an error signal when the second operating state does not match the predetermined criterion. In response to the error signal, power reduction stage 94 modifies P _{DEMAND (t)} in a non-linear manner and sets MP _{DEMAND (t)} to the prescribed low required power output P _LOW . If there is no error signal, the power reduction stage 94 holds the value of P _{DEMAND (t)} as the MP _{DEMAND (t)} value.

The value of P _LOW is determined to be greater than zero, but is preferably lower than the power level at the site where human tissue ablation is performed. In the preferred embodiment shown, P _LOW is about 1 watt.

The power reduction stage 94 sets the MP _{DEMAND (t)} value in a non-linear manner and returns it to the value of P _{DEMAND (t)} as soon as the operating condition causing the power reduction mode stops.

  In the preferred embodiment shown, the power reduction stage 94 corresponds to a specified power or temperature condition. FIG. 8 schematically illustrates a preferred embodiment of the power down stage 94.

The power down stage 94 includes microswitches 108 and 110. Microswitch 108 receives P _{DEMAND (t)} as an input from DPP 76 (see also FIG. 5). Microswitch 110 receives the value of P _LOW as input. Output line 120 connects converter 112 in parallel to the outputs of microswitches 108 and 110.

  The power down stage also includes three comparators 114, 116 and 118. Each comparator 114, 116 and 118 independently controls the microswitches 108 and 110 while taking into account various operating conditions.

In the preferred embodiment shown (see FIG. 8), the outputs of comparators 114, 116 and 118 are connected to OR gate 122. The output switch line S extends to the micro switch 108, while the negative switch line S _NEG reaches the micro switch 110. If no error signal comes from any of the comparators 114, 116 and 118 (when all operating conditions match the specified criteria), S = 1 (switch 108 is closed) and S _NEG = 0 (Open switch 110). If there is an error signal from any of the comparators 114, 116 and 118 (if at least one operating state does not match the specified criteria), S = 0 (open switch 108) and S _NEG = 1 (switch 110 is closed).

(A) Based on the maximum output state
The output of the comparator 114 takes into account the specified maximum power state. The comparator 114 receives the current instantaneous power P _(t) as its (+) input and the prescribed maximum power value P _MAX as its reciprocal or (−) input.

In this embodiment, the comparator 114 compares P _(t) with a specified maximum output value P _MAX . The state where there is no error is a case where P _(t) <P _MAX . In this state, the comparator 114 performs setting such that the micro switch 108 is closed and the micro switch 110 is opened. In this state, the micro switch 108 passes the value of P _{DEMAND (t)} as the output MP _{DEMAND (t)} .
The state where an error exists is a case where P _(t) ≧ P _MAX . In this state, the comparator 114 performs setting such that the micro switch 108 is opened and the micro switch 110 is closed. In this state, the micro switch 108 blocks the passage of the value of P _{DEMAND (t) and} sets P _LOW as the output MP _{DEMAND (t)} . In short, when P _(t) ≧ P _MAX , step 94 instantaneously reduces P _{DEMAND (t)} to P _LOW in a non-linear manner.

The value of P _MAX can vary depending on the special requirements of the ablation process.
The generator 12 may also have an interface 96 as part of its overall interface 13 for the physician to select and adjust P _MAX (see also FIG. 1).

In cardiac ablation, P _MAX increases as the surface of the ablation electrode expands, and P _MAX is believed to be in the region of about 50 watts to about 200 watts.

As FIG. 9 shows, the value of P _MAX is also not based on the direct power input set by the physician, but rather based on the physical or functional characteristics of the ablation electrode used, or both. Can be set on the basis.

  Examples of the physical or functional characteristics of the ablation electrode include the surface portion, the outer shape of the electrode, the directivity of the electrode, and the dispersion characteristics of the electrode field. For example, the electrode is normally expected to have a low power setting due to the smaller surface area.

The relationship between the type of electrode and P _MAX can be determined by a test that focuses on experiments and observations. The test results are copied to the survey power criteria table 102 and can be placed in the ROM of the generator 12 (as shown in FIG. 9).

In a preferred embodiment, the power down stage 94A has a register 98 for setting the P _MAX based on automatically written to investigate power reference table 102 transferred power criteria.

Resistor 98 has an input 100 (a portion of the generator's overall interface 13, see also FIG. 1) for inputting the type of electrode used by the physician. The register 98 then automatically sets P _MAX to the second process stage 58 based on the power reference table 102.

  Instead of doing this (as FIG. 9 shows), when the catheter 14 is connected to the generator 12, the catheter 14 can itself have a means of automatically generating an identification signal representing the electrode type. . The signal uniquely identifies a particular physical or performance characteristic of the connected electrode 16.

In this organization, the data acquisition element 106 interrogates and reads the catheter 14 identification signal to identify the electrode type. The element 106 then refers to the survey table 102 and automatically sets P _MAX via the register 98.

  There are various means for automatically generating an electrode type identification signal. FIG. 10 shows the desired organization.

In the illustrated embodiment, the catheter handle 20 has a resistor R with a defined ohm value. This R ohm value represents the sum of the calibration resistance value R _CAL (as previously described) and the selected add-on resistance value R ₁ . The calibration resistance R _CAL is a fixed value depending on the thermistor 34 in the catheter 14. The magnitude of the add-on resistance value R _I takes various values depending on the type of electrode within a predetermined increase amount.

For example, an add-on value R _I of 5000 ohms is assigned to a type 1 electrode. Also, type 2 electrodes are assigned an add-on value R _I of 10,000 ohms, type 3 electrodes are assigned an add-on value R _I of 15,000 ohms, and so on.

Assuming the fixed calibration resistance value R _c of the thermistor 34 is 4000 ohms, the handle 20 of the type 1 electrode will have a resistor R of 9000 ohms (4000 ohm calibration resistance R _c +5000 ohm add-on resistance) R _I ). The Type 2 electrode handle 20 has a 14,000 ohm resistor R (4000 ohm calibration resistance R _c +10,000 ohm add-on resistance R _I ), and the Type 3 electrode handle 20 has a 19,000 ohm resistor R (4000 ohm Calibration resistance R _c + 15,000 ohm add-on resistance R _I ).

The survey table 104 (shown in FIG. 9) in the data acquisition element 106 stores the calibration resistance constant R _CAL , the area of the add-on resistance R _I is the identified electrode type, and their total (the system actually Corresponding to the value of register R to be sensed).

  When connected to the generator 12, the element 106 senses the total ohm value of the resistor R in the handle 20. Element 106 references survey table 104. In the survey table 104, the total resistance R sensed as less than 10,000 ohms is identified as a type 1 electrode, the total resistance R sensed as 10,000 to 15,000 ohms is identified as a type 2 electrode, and A total resistance R sensed as greater than 15,000 ohms and within 20,000 ohms is identified as a Type 3 electrode.

The element 106 then refers to the power reference survey table 102 to obtain the corresponding power state. Register 98 automatically sets the P _MAX at power down stage 94A.

With further reference to the survey table 104, the data acquisition element 106 subtracts a known add-on value according to the identified electrode type. In this method, the generator 12 also derives the value of the calibration resistance R _CAL of the thermistor 34. As already mentioned (and as shown in FIG. 5), the first process stage 56 processes the calibration resistance and the resistance sensed by the thermistor to derive the temperature T _{M (t)} as described above. .

  In alternative embodiments (not shown), instead of register R, the handle can have a solid microchip, ROM, EEROM, EPROM, or non-volatile RAM.

  The microchip can be preprogrammed with digital values that appropriately represent the calibration resistance of the thermistor 34 (or the calibration resistance of multiple thermistors) and the type of electrode. In this organization, the microchip outputs those values to the register 98 when requested by the data acquisition element 106.

(B) Based on maximum absolute temperature condition
The output of comparator 116 is responsive to a specified maximum absolute temperature condition. Comparator 116 receives temperature value T _{PRED (t)} from PTP 70 at its (+) input. The comparator 116 receives the specified maximum temperature value T _MAX as its reciprocal or (−) input.

In this embodiment, the comparator 116 compares T _{PRED (t)} with a specified maximum temperature value T _MAX . In the case of no error state, T _{PRED (t)} <T _MAX . In this state, the comparator 116 is set to close the microswitch 108 and open the microswitch 110. In this state, the micro switch 108 passes the value of P _{DEMAND (t)} as the output MP _{DEMAND (t)} .

The state where an error exists is when T _{PRED (t)} ≧ T _MAX . In this state, the comparator 116 opens the micro switch 108 and closes the micro switch 110. In this state, the micro switch 108 blocks the passage of the value of P _{DEMAND (t)} and P _LOW becomes the output MP _{DEMAND (t)} . In short, when T _{PRED (t)} ≧ T _MAX , step 94 instantaneously non-linearly decreases P _{DEMAND (t)} for P _LOW .

The value of T _MAX is defined in various ways. For example, the value may be a selected absolute value entered by a physician. For cardiac ablation, the value of T _MAX is in the region between 80 ° C. and 95 ° C., and approximately 90 ° C. is considered a desirable typical value.

(C) Based on maximum absolute temperature condition
The output of the comparator 118 is responsive to a specified increased temperature state T _INCR according to the following equation based on T _SET .

T _INCR = T _SET + INCR
Here, INCR is a preselected increase amount.

INCR takes various values, also T _SET may also take just as different values. Both are based on physician judgment and empirical data. Typical values for INCR in cardiac ablation are in the range of 2 ° C. to 8 ° C., desirably about 5 ° C.

Comparator 116 receives temperature value T _{PRED (t)} from PTP 70 at its (+) input, as in comparator 114. The comparator 116 receives the specified increased temperature value T _INCR as its reciprocal or (−) input.

In this embodiment, the comparator 116 compares T _{PRED (t)} with a specified increased temperature value T _INCR . The error-free state is when T _{RPED (t)} <T _INCR . In this state, the comparator 116 performs setting such that the micro switch 108 is closed and the micro switch 110 is opened. In this state, the micro switch 108 passes the value of P _{DEMAND (t)} as the output MP _{DEMAND (t)} .

The state where an error exists is a case where T _{PRED (t)} ≧ T _INCR . In this state, the comparator 116 sets the micro switch 108 to open and the micro switch 110 to close. In this state, the micro switch 108 blocks the passage of the value of P _{DEMAND (t)} and P _LOW becomes the output MP _{DEMAND (t)} . In short, when T _{PRED (t)} ≧ T _INCR , step 94 instantaneously reduces P _{DEMAND (t)} to P _LOW in a non-linear manner.

(D) Generation of required voltage
If any of the comparators 114, 116 or 118 opens the switch 108 and closes the switch 110 (ie when at least one error condition exists), P _LOW instantaneously MP _{DEMAND (t)} Set as Under this condition, the converter 112 receives P _LOW as MP _{DEMAND (t)} . If none of comparators 114, 116, and 118 open switch 108 and switch 110 is closed, converter 112 receives P _{DEMAND (t)} as MP _{DEMAND (t)} .

There are various ways in which the converter 112 of the second process stage 58 generates V _{DEMAND (t)} and adjusts P _(t) . For example, the converter 112 can adopt a proportional control principle, a proportional integral derivative (PID) control principle, a neural network, a fuzzy logic, an adaptive control principle, or the like.

In one embodiment, the converter 112 employs known PID principles to derive V _DEMAND . In this embodiment, converter 112 compares MP _{DEMAND (t)} with the generated power signal P _(t) obtained from multiplier 60. In this embodiment, converter 112 also takes into account continuous changes in the generated power signal P _(t) . Based on these conditions, the converter 112 in the second process stage 58 derives the required voltage signal V _DEMAND .

Instead of this, the converter 112 can directly convert MP _{DEMAND (t)} to the required voltage V _{DEMAND (t)} according to the following equation by using the proportional control principle.

Where Z _(t) is the sensed system impedance and V _{DEMAND (t)} is the RMS value of the output voltage.

(E) Impedance monitoring
For this and other purposes, the generator 12 is desired to have an impedance microprocessor 88. The impedance microprocessor 88 receives the instantaneous power signal I _(t) and the instantaneous voltage signal V _(t) from the sensing transformers 62 and 64 as already defined values. The microprocessor 88 derives the impedance Z _(t) (ohm value) according to the following equation.

Preferably, the generator 12 has a display 90 as part of its overall interface 13 and wants to show the measured impedance Z _(t) (see also FIG. 1).

The microprocessor 88 also generally maintains a record of the overtime of the sampled impedance Z _(t) . This causes the microprocessor to calculate the change in impedance during the selected interval and generate an appropriate control signal based on a predetermined criterion. Even if the power reduction stage 94 sets P _{DEMAND (t)} as P _LOW and stops tissue ablation, the microprocessor continues to play a role to be continuously set for process Z _(t) thereafter. .

  For example, even if the measured impedance exceeds a predetermined setting range, the microprocessor 88 generates a command signal and stops supplying power to the ablation electrode 16. The impedance setting range for cardiac ablation is considered to be about 50 to 300 ohms.

  The most likely possibility is the formation of coagulation on the ablation electrode 16 when the impedance begins to increase continuously beyond that set range. It is considered that a sudden increase in impedance exceeding the set range is a result of sudden formation of coagulation or a sudden change in the position of the ablation electrode 16. The sudden change in impedance can also be attributed to inadequate contact between the ablation electrode 16 and the tissue of interest. Everything needs immediate attention. For example, it is necessary to take out and clean the ablation electrode 16 or replace the ablation electrode 16.

  The generator 12 has a visible and audible alarm 92 as part of its overall interface 13 (see also FIG. 1) and it is desirable to communicate a warning to the user when these impedance related conditions occur.

  When a very high impedance value is generated, there may be insufficient contact with the neutral electrode 18 in the skin or an electrical problem in the generator 12. Again, this tells us that it needs to be dealt with immediately.

(F) Error cutoff mode
Even if the power reduction stage 94 is suddenly reduced, the power supply is not stopped based on the provision of instantaneous high power or high temperature. In the preferred embodiment shown, the second process stage 58 also has an error blocking stage 128. This error block stage 128 corresponds to a sustained overtemperature condition over a set period or a system fault condition that has occurred or is occurring. The error cut-off phase 126 stops power supply to all the electrodes 16. The error cut-off phase 128 can work separately from the power down mode.

For example, as long as T _{PRED (t)} exceeds T _SET by less than INCR, power reduction stage 94C will not set P _LOW . However, if this over-temperature condition lasts longer than a specified period (eg 2 to 5 seconds), the second process stage 58 is assumed to be a production or developing system failure, and a condition to initiate a power shutdown Can be.

According to other example methods, if T _{PRED (t)} ≧ T _MAX or T _INCR , the power reduction stage 94B or power reduction stage 94C is a motivation for setting P _LOW . If this overtemperature condition persists during a power down condition for a specified period of time (eg, 2 to 5 seconds), the second process stage 58 has occurred or is about to occur It is assumed that power interruption should be started.

  The generator 12 provides control over the ablation process based on the rules. Power monitoring and control ensures an effective supply of radio frequency energy to the ablation electrode 16 during the setting of stable physiological limits.

  Generator 12 also has an alternative control mode based on power. In this mode, the generator 12 strives to maintain the set power state regardless of the measured temperature state. The generator 12 may switch to a power control mode, for example when the electrode 16 in use does not have a temperature sensing element 30 or, if there is a temperature sensing element 30 on the electrode 16, at the physician's choice.

  The preferred embodiment shown implies that information analysis and feedback signal generation can be achieved through the use of a microprocessor controlled by components utilizing digital processing. Other logic control circuits utilizing microswitches, AND / OR gates, inventors, etc. should be evaluated as equivalent to the techniques shown in the microprocessor and preferred embodiments for controlling the components.

Various features of the invention are set forth in the following claims.
The present invention can be embodied in several forms without departing from its nature or important characteristics. The scope of the present invention is defined by the appended claims, and not by the specific description preceding the claims. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims.

FIG. 1 is a perspective view of a tissue ablation system having an energy emitting electrode and an energy generator coupled thereto. 2, 3, and 4 are each provided with a temperature sensing unit, and an elevational view, an end view, and a cross-sectional view of the system-related electrode shown in FIG. A surface cut along the surface). 2, 3, and 4 are each provided with a temperature sensing unit, and an elevational view, an end view, and a cross-sectional view of the system-related electrode shown in FIG. A surface cut along the surface). 2, 3, and 4 are each provided with a temperature sensing unit, and an elevational view, an end view, and a cross-sectional view (on line 4-4 in FIG. 3) of the electrodes related to the system shown in FIG. 1. A surface cut along the surface). FIG. 5 is a schematic diagram of a generator for supplying energy to the electrodes in the system shown in FIG. This generator utilizes special modified PID control technology to maintain the required set temperature by changing power in response to the sensed temperature. 6A and 6B are graphs showing a curve of a set temperature state that the generator continuously maintains. FIG. 7 is a schematic diagram of an alternative system for use in connection with the generator shown in FIG. 5, which uses adaptive control techniques to change the adaptive power in response to the sensed temperature. FIG. 8 is a schematic diagram of a system in use in connection with the generator shown in FIG. 5, which scales down the power in response to either a specified power or temperature condition. FIG. 9 is a schematic diagram of a system in use related to the generator shown in FIG. 5, which establishes the highest power state for use by the power scaleback system shown in FIG. FIG. 10 is a schematic diagram showing a more detailed example of the system shown in FIG. 9, which automatically establishes the maximum power state based on the physical characteristics of the ablation electrode. FIG. 11A / B is a schematic diagram of an embodiment of a neural net prediction instrument that maintains the required set temperature by changing the power in response to the prediction of the highest tissue temperature. FIG. 11A / B is a schematic diagram of an embodiment of a neural net prediction instrument that maintains the required set temperature by changing the power in response to the prediction of the highest tissue temperature. FIG. 12 is a schematic diagram of an embodiment of fuzzy logic that maintains the required set temperature state.

Claims (1)

Device as described in the examples.

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